U.S. patent number 10,150,280 [Application Number 14/276,869] was granted by the patent office on 2018-12-11 for apparatus for fabrication of three dimensional objects.
This patent grant is currently assigned to HOLO, INC.. The grantee listed for this patent is Holo, Inc.. Invention is credited to Arian Aghababaie, Pierre Lin.
United States Patent |
10,150,280 |
Aghababaie , et al. |
December 11, 2018 |
Apparatus for fabrication of three dimensional objects
Abstract
An apparatus for bottom-up fabrication of three dimensional
objects, the apparatus comprising: a vat for a photosensitive
polymer, the floor of the vat including a working surface arranged
such that, in use, light incident on the working surface interacts
with the photosensitive polymer at the working surface to fabricate
a portion of the three dimensional object; a build platform capable
of being inserted into the vat, the build platform having a planar
surface; an elevator mechanism capable of adjusting the separation
between the working surface of the vat and the planar surface of
the build platform; and a rotation mechanism capable of varying the
relative rotational position of the vat relative to the build
platform, the relative rotation being about an axis which is normal
to the working surface of the vat.
Inventors: |
Aghababaie; Arian (London,
GB), Lin; Pierre (London, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
Holo, Inc. |
San Francisco |
CA |
US |
|
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Assignee: |
HOLO, INC. (Oakland,
CA)
|
Family
ID: |
48700769 |
Appl.
No.: |
14/276,869 |
Filed: |
May 13, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20140339741 A1 |
Nov 20, 2014 |
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Foreign Application Priority Data
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May 14, 2013 [GB] |
|
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1308662.4 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C
64/20 (20170801); B29C 64/255 (20170801); B29C
64/124 (20170801); B33Y 30/00 (20141201); B29C
64/241 (20170801); B29K 2883/00 (20130101) |
Current International
Class: |
B29C
67/00 (20170101); B29C 64/20 (20170101); B33Y
30/00 (20150101); B29C 64/124 (20170101); B29C
64/255 (20170101) |
References Cited
[Referenced By]
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WO 2008/055533 |
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WO 2010/045951 |
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Other References
International Search Report and Written Opinion received for
International Patent Application No. PCT/US2014/37998, filed May
14, 2014. dated Sep. 4, 2014. 10 pages. cited by applicant .
Examination Report under Section 18(3) in Great Britain priority
Application No. 1308662.4, dated Jul. 14, 2016, 3 pages. cited by
applicant .
Search Report in Great Britain Application No. 1308662.4, filed
Mar. 14, 2013. dated Nov. 13, 2013. 1 page. cited by applicant
.
Dendukuri, et al. Continuous-Flow Lithography for High-Throughput
Microparticle Synthesis. Nature Materials, vol. 5, May 2006. pp.
365-369. cited by applicant .
Communication pursuant to Article 94(3) EPC in Application No. EP
14 797 164.2, dated Mar. 3, 2017, 6 pages. cited by applicant .
Supplementary European Search Report in Application No. EP 14 79
7164.2, dated Nov. 2, 2016, 6 pages. cited by applicant .
Authorized officer Kihwan Moon, International Preliminary Report on
Patentability in PCT/US2014/037998, dated Nov. 26, 2015, 8 pages.
cited by applicant.
|
Primary Examiner: Gupta; Yogendra N
Assistant Examiner: Le; Ninh
Attorney, Agent or Firm: Wilson Sonsini Goodrich &
Rosati
Claims
The invention claimed is:
1. An apparatus for bottom-up fabrication of three dimensional
objects, the apparatus comprising: a vat for a photosensitive
polymer, a floor of the vat including a working surface arranged
such that, in use, light incident on the working surface interacts
with the photosensitive polymer at the working surface to fabricate
a portion of the three dimensional object; a build platform
configured to be inserted into the vat, the build platform having a
planar surface; an elevator mechanism configured to adjust a
separation between the working surface of the vat and the planar
surface of the build platform; and a rotation mechanism configured
to vary a relative rotational position of the vat relative to the
build platform, the relative rotational position being about an
axis which is normal to the working surface of the vat; wherein the
floor includes a first floor portion of a first thickness and a
second floor portion of a second thickness, the second thickness
being less than the first thickness; wherein the first floor
portion has a first vertical side, the second floor portion has a
second vertical side, and the first vertical side directly contacts
the second vertical side, and wherein the rotation mechanism is
configured to vary the relative rotational position about the axis
between a first position and a second position, the first position
locating the first floor portion under the planar surface of the
build platform to fabricate the portion of the three dimensional
object at the working surface, and the second position locating the
second floor portion under the planar surface to increase a depth
of the photosensitive polymer between the portion of the three
dimensional object and the floor of the vat.
2. The apparatus of claim 1, wherein the rotation mechanism is
arranged to vary the rotational position of the vat.
3. The apparatus of claim 2, wherein the rotation mechanism is a
rotatable plate upon which the vat is mounted.
4. The apparatus of claim 3, wherein the vat includes a plug and
the rotatable plate includes an aperture, the plug being configured
to engage the aperture to secure the vat to the rotatable
plate.
5. The apparatus of claim 1, wherein the rotation mechanism is
arranged to vary the rotational position of the build platform.
6. The apparatus of claim 1 further comprising a heating element in
thermal contact with the vat.
7. The apparatus of claim 1 wherein the floor of the vat has a
thickness of at least 5 mm.
8. The apparatus of claim 1, wherein the first floor portion has a
thickness of at least 6 mm and the second floor portion has a
thickness of at least 5 mm.
9. The apparatus of claim 1 wherein the vat is formed entirely of a
liquid silicone rubber.
10. The apparatus of claim 1, wherein the vat is made of optically
clear material comprising a thermoplastic and is not made entirely
of a liquid silicone rubber, and the first floor portion comprises
a replaceable optically clear silicone pad comprising the first
vertical side and the working surface.
11. An apparatus for bottom-up fabrication of three dimensional
objects, the apparatus comprising: a vat for a photosensitive
polymer, a floor of the vat including a working surface arranged
such that, in use, light incident on the working surface interacts
with the photosensitive polymer at the working surface to fabricate
a portion of the three dimensional object; a build platform
configured to be inserted into the vat, the build platform having a
planar surface; an elevator mechanism configured to adjust a
separation between the working surface of the vat and the planar
surface of the build platform; and a rotation mechanism configured
to vary a relative rotational position of the vat relative to the
build platform, the relative rotational position being about an
axis which is normal to the working surface of the vat; wherein the
floor includes a first floor portion of a first thickness and a
second floor portion of a second thickness, the second thickness
being less than the first thickness; and wherein the rotation
mechanism is configured to vary the relative rotational position
about the axis between a first position and a second position, the
first position locating the first floor portion under the planar
surface of the build platform to fabricate the portion of the three
dimensional object at the working surface, and the second position
locating the second floor portion under the planar surface to
increase a depth of the photosensitive polymer between the portion
of the three dimensional object and the floor of the vat.
12. The apparatus of claim 11, wherein the rotation mechanism is
arranged to vary the relative rotational position of the vat.
13. The apparatus of claim 12, wherein the rotation mechanism is a
rotatable plate upon which the vat is mounted.
14. The apparatus of claim 13, wherein the vat includes a plug and
the rotatable plate includes an aperture, the plug being configured
to engage the aperture to secure the vat to the rotatable
plate.
15. The apparatus of claim 11, wherein the rotation mechanism is
arranged to vary the rotational position of the build platform.
16. The apparatus of claim 11, further comprising a heating element
in thermal contact with the vat.
17. The apparatus of claim 11, wherein the floor of the vat has a
thickness of at least 5 mm.
18. The apparatus of claim 11, wherein the first floor portion has
a thickness of at least 6 mm and the second floor portion has a
thickness of at least 5 mm.
19. The apparatus of claim 11, wherein the vat is formed entirely
of a liquid silicone rubber.
20. The apparatus of claim 11, wherein the vat is made of optically
clear material comprising a thermoplastic and is not made entirely
of a liquid silicone rubber, and the first floor portion comprises
a replaceable optically clear silicone pad comprising the working
surface.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.K. Patent Application No.
1308662.4, filed on May 14, 2013, the entire contents of which are
hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to an apparatus for bottom-up
fabrication of three dimensional objects.
BACKGROUND OF THE INVENTION
Additive manufacturing (also known as 3D printing, solid free-form
fabrication, rapid prototyping and rapid manufacturing) is commonly
used to manufacture three-dimensional solid objects. It is
particularly useful for applications where speed of manufacture is
important but where low costs are desirable, for example in the
manufacture of prototypes.
The additive manufacturing process involves the creation of a three
dimensional object by successive addition of multiple material
layers, each layer having a finite thickness. A variety of methods
fall under the umbrella of additive manufacturing including:
stereolithography (SLA), fused deposition modelling (FDM),
selective deposition modelling (SDM), laser sintering (LS) and
selective light modulation (SLM).
Each of the above known methods includes the following steps:
1. The conversion of a computer-generated 3D model to a file format
(such as .STL or .OBJ) which provides geometric information in a
physical Cartesian space. Computer aided design (CAD) software may
be used to generate the initial 3D model.
2. Once converted, the 3D model is broken down ("sliced") into a
series of two-dimensional (`2D`) discrete cross sections.
3. A computer controlled apparatus successively fabricates each
cross section, one on top of another in the z-direction, forming
successive layers of build material on top of another which in turn
forms the three dimensional object.
The fabrication process differs between the above-mentioned
methods, as does the choice of build material.
The fabrication process used in both stereolithography (SLA) and
selective light modulation (SLM) involves a build material of
liquid photosensitive polymer (often known as a `resin`) and a
mechanism for exposing the photosensitive polymer to
electromagnetic radiation.
Exposed photosensitive polymer undergoes a chemical reaction
leading to polymerization and solidification. The solidification of
the photosensitive polymer is commonly known as "curing", and the
solidified photosensitive polymer is said to have been "cured" or
"hardened".
In both SLA and SLM, electromagnetic radiation is applied to a
targeted area known as the "working surface". However, the two
processes differ from one another in the way that the
electromagnetic radiation is applied to the targeted area: SLA
systems use a laser beam mounted on an x-y scanning system to
create each material layer of the 3D object by tracing a digital
cross-section onto the photosensitive polymer; SLM systems on the
other hand, use spatial light modulators such as digital projectors
to project the whole digital cross-section onto the photosensitive
polymer in one go. The digital projector may be based on: Digital
Light Processing (DLP), Digital Micromirror Device (DMD), Liquid
Crystal Display (LCD), or Liquid Crystal on Silicon (LCOS).
The apparatus required to carry out SLA or SLM methods usually
includes: a vat to hold the photosensitive polymer; a source of
electromagnetic radiation (typically UV, near-UV, or visible
light); a build platform; an elevator mechanism capable of
adjusting the separation of the vat and the build platform; and a
controlling computer.
The apparatus may be configured in a "top-down" arrangement in
which the source of electromagnetic radiation is located above the
vat, or in a "bottom-up" arrangement where the source of
electromagnetic radiation is located below the vat.
In a top-down arrangement, such as that shown in FIG. 1A, the
source of the electromagnetic radiation is located above the vat.
In use, the build platform is positioned below the surface of the
photosensitive polymer. The working surface is the photosensitive
polymer located above the build platform and the distance between
the upper surface of the photosensitive polymer and the upper
surface of the build platform defines the cross-sectional thickness
of a cured layer. Disadvantages associated with the top-down method
include the necessary process of recoating the cured photosensitive
polymer with uncured ("fresh") photosensitive polymer. In addition,
the high viscosity of the photopolymer and high surface tension can
lead to difficulties in levelling the surface of the photosensitive
polymer.
In a bottom-up arrangement, such as that shown in FIG. 1B, the
issue of levelling the surface of the photosensitive polymer is
avoided by locating the source of electromagnetic radiation below
the vat. A layer of photosensitive polymer sandwiched between an
optically clear vat floor and the build platform forms the working
surface and allows for precise control over the layer thickness and
the surface quality of the layer of photopolymer. However, as the
photosensitive polymer hardens, it bonds to those surfaces it is in
contact with resulting in high separation forces and difficulties
in raising the build platform to build the next layer and a risk of
damaged to the cured layer.
It is known that damage during separation can be reduced by
non-stick coatings and/or thin film layers on the vat. However,
these coatings and layers add to the cost of the 3D printing
equipment.
Dendukuri, et al (2006), Nature Mater., Vol. 5, pp. 365-369
suggested the application of coatings that inhibit the cure of the
photosensitive polymer to the vat floor. A coating of PDMS (an
optically clear oxygen rich resin) is applied to the bottom of the
vat, the presence of oxygen inhibits the cure of acrylate polymers
thus creating a layer of uncured liquid polymer (approximately
2.5.mu. thick) between the PDMS and the solidified layer. As a
result the cured layer does not adhere to the vat floor thus
reducing the forces required to raise the elevator. However, when
using a cure-inhibition coating, the separation forces between the
vat floor and the cured part can be still be very large due to the
surface tension forces associated with thin-film viscous liquids.
The surface tension forces are particularly important because they
are inversely proportional to the layer thickness.
One method of overcoming damage due to surface tension forces is
x-translation which utilises a cure-inhibition coating with a slide
mechanism and variable depth vat. The cure inhibition coating on
the vat floor creates a non-cured layer that acts as a lubricant
between the vat floor and the cured part thus the cured part can
easily glide on the cure-inhibition layer. The cured cross-section
is slid off the cure-inhibition layer into a deeper channel,
increasing the distance between the solidified part and the vat
floor, reducing surface tension forces by an order of magnitude,
allowing the build platform to be raised easily before being moved
back to a position above the build platform. This method of
translating the build platform from a shallow channel to a deeper
channel via translation in the x-direction typically requires an
additional "over-lift" step, where the build platform is raised
higher than necessary in order to allow for photosensitive polymer
to recoat the working surface. Any such additional step/extra
movement leads to an undesirable build-up in the time taken to
prepare the working surface for the next layer.
As 3D models are sliced into thousands of material layers, it is
important to reduce the fabrication time of each cross-section.
This depends upon a number of factors such as the time to cure the
photosensitive polymer at the desired thickness and the time to
prepare the working surface for the next layer. The time to cure
the photosensitive polymer is a function of the power of the source
of the electromagnetic radiation at the working surface and the
composition of the photosensitive polymer. Typically, high power
sources result in shorter cure times. The time taken to prepare the
working surface for the next layer typically depends on the
separation method and time taken to recoat the working surface with
fresh photosensitive polymer. Several extra seconds taken during
the layer separation process for a model with thousands of layers
will add extra hours onto the overall fabrication time.
The apparatus used in the above described SLA and SLM methods tend
to be mechanically complex, difficult to operate and maintain and
expensive to buy and use. The use of high power lasers and UV light
sources tends to significantly increase the cost of the machines
both to purchase and to use through high-energy consumption.
Furthermore, the health and safety risks of high power laser and UV
light source make current systems unsuitable for home use or by
untrained personnel.
SUMMARY OF THE INVENTION
According to a first aspect, the present invention aims to solve
the above problems by providing an apparatus for bottom-up
fabrication of three dimensional objects, the apparatus comprising:
a vat for a photosensitive polymer, the floor of the vat including
a working surface arranged such that, in use, light incident on the
working surface interacts with the photosensitive polymer at the
working surface to fabricate a portion of the three dimensional
object; a build platform capable of being inserted into the vat,
the build platform having a planar surface; an elevator mechanism
capable of adjusting the separation between the working surface of
the vat and the planar surface of the build platform; and a
rotation mechanism capable of varying the relative rotational
position of the vat relative to the build platform, the relative
rotation being about an axis which is normal to the working surface
of the vat.
In addition to providing a mechanism by which the build platform
can be moved over the deeper channel (thereby reducing the
separation forces), the rotational movement causes the liquid
photopolymer to re-coat the print area. This means that there is no
need for an additional "over lift" step to ensure re-lamination of
the photosensitive polymer. The relative rotation therefore results
in a reduction of the number of steps required whilst still
ensuring adequate re-lamination. By reducing the number of steps
required, the relative rotation results in a more efficient
apparatus.
Another advantage of the relative rotation mechanism is that it
reduces the mechanical complexity of the apparatus as compared for
example to the x-translation method. With x-translation a second
linear actutation system is required comprising of a stepper motor,
linear actutator etc. This system has to be either attached to the
z-axis elevator so that the build platform can move in the
x-direction or fixed to the machince such that the vat moves in the
x-direction and the build platform is fixed. Linear actuation
systems are complex and expensive compared to rotation actuation
systems.
Optional features of the invention will now be set out. These are
applicable singly or in any combination with any aspect of the
invention.
Optionally, the rotation mechanism is arranged to vary the
rotational position of the vat.
In this way it is not necessary to translate the build platform in
the x-direction. This is a mechanical advantage as the mechanical
drive needed to rotate the vat is advantageously simple compared
with the mechanical drive that would be necessary to translate the
build platform in the x-direction.
Optionally, the rotation mechanism is a rotatable plate upon which
the vat is mounted.
Optionally, the vat includes a plug and the rotatable plate
includes an aperture, the plug being configured to engage the
aperture to secure the vat to the rotatable plate.
Optionally, the rotation mechanism is arranged to vary the
rotational position of the build platform.
Preferably, the apparatus further comprises a heating element in
thermal contact with the vat.
In this way, the photosensitive polymer can be heated during the
additive manufacturing process. This reduces the photo energy
required to solidify the polymer and therefore reduces the time to
solidify each layer.
Furthermore, surface tension decreases with increasing temperature
so the presence of a heating element can further reduce undesirable
separation forces.
Additionally, viscosity of the photosensitive polymer decreases
with temperature. A decrease in the viscosity of the photosensitive
polymer is desirable because it means that re-coating of the
working surface is easier.
The heating element is preferably placed underneath the vat. In
this way it is out of contact with the polymer and maintenance of
the system is therefore reduced.
Preferably the floor has a thickness of at least 5 mm. In this way,
the vat holds its shape itself so that no supporting structure is
needed for this purpose.
Even more preferably the entire floor of the vat has thickness of
at least 5 mm.
Even more preferably, the entire floor of the vat and the
surrounding walls of the vat have a thickness of at least 5 mm.
Preferably, the floor of the vat includes a first floor portion of
a first thickness and a second floor portion of a second thickness,
the second thickness being less than the first thickness; such that
the first floor portion defines a raised working surface.
In this way, the first floor portion defines a raised working
surface. In other words, a variable thickness vat is formed with
the working surface raised above the rest of the floor of the vat.
This creates a two-channel vat with a shallow and a deep channel.
The separation force due to surface tension of the liquid polymer
is inversely proportionally to the thickness of the liquid thus if
the build platform is moved from the shallow to the deep channel
the separation forces can be greatly reduced, therefore allowing
the elevator mechanism to be lightweight and a low torque motor to
be used, thus saving space and reducing the power consumption of
the machine. Furthermore, the light loads on the elevator reduce
the wear and tear on the drive mechanism thus prolonging the
life-span of the mechanism.
Preferably, the first floor portion has a thickness of at least 6
mm and the second floor portion has a thickness of at least 5
mm.
Optionally, the vat is formed entirely of a liquid silicone
rubber.
In this way, the material of the vat inhibits the cure of acrylate
polymers. This means that after exposure of the photosensitive
polymer at the working surface, the liquid silicone rubber results
in a lubricating layer of liquid polymer between the vat and the
solidified layer of the three dimensional object formed by the
exposed photosensitive polymer. This means that during relative
rotation of the vat relative to the build platform, the solidified
part will glide on the surface of the silicone with virtually no
shear forces. This enables even delicate parts of a three
dimensional object to be fabricated with a reduced risk of
damage.
In addition, the use of solid liquid silicone rubber means that the
vat is more resilient than a non-silicone vat than has been coated
with a PDMS like coating because liquid silicone rubber has a much
greater tear strength and hardness. PDMS coatings tend to become
damaged over time and need to be replaced. Leakage of
photosensitive polymer through a damaged PDMS coating can also
necessitate the replacement of the entire vat. The use of liquid
silicone rubber to create the entire vat therefore reduces
maintenance and increases the life span of the vat.
Furthermore, the use of liquid silicone rubber simplifies
fabrication because the vat can be injection moulded in one piece.
The part count and manufacturing complexity is significantly
reduced.
Additional benefits of using a silicone vat are ease of maintenance
as the whole vat inhibits the cure of the photopolymer and
therefore excess polymer can be easily removed. A liquid silicone
vat has a reduced risk of damage during use or whilst in transit
compared to solid vats due to the silicone's inherent flexible
properties.
Furthermore, silicone rubber has a high temperature resistance
allowing for the use of heating elements to further increase the
reactivity of the polymer and to reduce its viscosity; both of
which are desirable.
Optionally, the working surface of the vat is a replaceable
optically clear silicone pad. In this way, the working surface can
be easily removed in the event that it becomes damaged.
The optically clear silicone pad preferably has a thickness of at
least 5 mm.
According to a second aspect of the present invention, there is
provided a vat for bottom-up fabrication of three dimensional
objects, the vat formed entirely of a liquid silicone rubber.
Advantages associated with this vat are discussed above.
According to a third aspect of the present invention, there is
provided a vat for bottom-up fabrication of three dimensional
objects, the vat including a replaceable optically clear silicone
pad. Advantages associated with this vat are discussed above.
According to a fourth aspect of the present invention, there is
provided an apparatus for bottom-up fabrication of three
dimensional objects, the apparatus comprising: a vat for a
photosensitive polymer, the floor of the vat including a working
surface arranged such that, in use, light incident on the working
surface interacts with the photosensitive polymer at the working
surface to fabricate a portion of the three dimensional object; a
build platform capable of being inserted into the vat, the build
platform having a planar surface; an elevator mechanism capable of
varying the separation between the working surface of the vat and
the planar surface of the build platform; and a heating element in
thermal contact with the vat.
Preferably, the apparatus further comprises a motorized plate
capable of moving the vat relative to the build platform along a
direction which is different to the direction of separation
provided by the elevator mechanism; wherein the heating element is
located between the motorized plate and the vat.
According to a fifth aspect of the present invention there is
provided an apparatus for bottom-up fabrication of three
dimensional objects including a source of electromagnetic radiation
having a wavelength of 405 nm.
Preferably, the source of electromagnetic radiation is a 405 nm
LED.
In this way, standard DMDs (with a low power 405 nm LED) found
within home-entertainment digital projectors can be used; there is
no need for expensive DMDs that have been developed specially for
use with high-power UV light. Also, low-power 405 nm LEDs are
cheaper than high power UV LEDs, UV bulbs, metal halide bulbs or
lasers.
Low power 405 nm LEDs have typical power values of between 2-10 W.
Low power UV LEDs of a similar optical power are considerably more
expensive. Furthermore, a UV specific DMD is required for
wavelengths below 400 nm and these are typically an order of
magnitude more expensive than standard DMDs.
High power UV LEDs have typical power values of 20-100 W and
require extensive thermal management which significantly increases
the cost of the projection electronics. Like the low power UV LEDs
they also require a UV specific DMD.
UV or metal halide bulbs have typical power values of hundreds of
Watts. They also have a reduced lifespan compared to LEDs. A Metal
halide bulb will typically have to be replaced after 2,000-3,000
hours of use whereas an LED has a typical life span of
approximately 20,000 hours.
Furthermore the optical power output of metal halide bulbs will
degrade over time thus reducing the power output and increasing
exposure times and hence print times. Optical output of LEDs will
not degrade over their lifespan. In addition, low power LEDs are
more energy efficient than high power UV LEDs or UV bulbs or
lasers, resulting in a significant reduction in running costs.
In addition, the use of a low-power 405 nm LED is advantageous due
to the reduced health and safety risk as compared to high powered
UV LEDs and UV lasers. this means that the apparatus can be
operated without significant health and safety-training and is
therefore more suitable for home environments. The power output of
laser can be as low 30 mW. However, as the size of the beam is very
small (300 Microns in diameter) the power/unit area is high which
means that they pose a significant risk to the eyes of a user (IEC
60825-1 Standard Class 3B Hazard).
According to a sixth aspect of the present invention, there is
provided a method of bottom-up fabrication of three dimensional
objects, the method comprising the steps of: providing a vat
containing photosensitive polymer, the floor of the vat including a
working surface; providing a build platform capable of being
inserted into the vat, the build platform having a planar surface;
positioning the build platform within the vat to create a layer of
photosensitive polymer between the planar surface of the build
platform and the working surface of the vat; exposing a region of
the layer of photosensitive polymer to electromagnetic radiation to
cure the exposed region; separating the cured photosensitive
polymer from the working surface of the vat by rotating the working
surface of the vat relative to the planar surface of the build
platform, the rotation being about an axis which is normal to the
working surface of the vat.
Further optional features of the invention are set out below.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described by way of
example with reference to the accompanying drawings in which:
FIG. 1A shows a cross section of a top-down prior art arrangement
and FIG. 1B shows a bottom-up prior art arrangement.
FIG. 2 shows a cross section of an apparatus according to a first
embodiment of the present invention.
FIG. 3A shows a cross section of a first vat and FIG. 3B shows a
cross section of a second vat.
FIGS. 4A, 4B, 4C, and 4D illustrates the apparatus of FIG. 1 at
various stages of use.
FIG. 5 shows a cross section of an apparatus according to a second
embodiment of the present invention.
FIG. 6 shows a cross section of a third embodiment of the present
invention.
FIG. 7 shows a cross section of a fourth embodiment of the present
invention.
FIGS. 8A, 8B and 8C show schematic views taken from above of the
apparatus of FIG. 7.
FIGS. 9A, 9B and 9C show cross sections of a third vat.
DETAILED DESCRIPTION
With reference to FIGS. 2, 3 and 4, the apparatus for bottom-up
fabrication of three dimensional objects includes a vat 13 for a
photosensitive polymer 16, a build platform 17 an elevator
mechanism 19 and a rotation mechanism 7.
The floor of the vat includes a working surface 14 at which light
from a light source 21 incident on the working surface interacts
with photosensitive polymer 16 at the working surface to fabricate
a portion of the three dimensional object.
The build platform has a planar surface 26, and the elevator
mechanism 19 is arranged to hold the build platform above the vat
such that when the working surface of the vat is located directly
underneath the build platform, the planar surface of the build
platform is parallel with the working surface 14.
The build platform 17 is the part onto which the cured
cross-sections are built. The build platform 17 is attached to the
elevator mechanism 19 by a quick release mechanism 18. The elevator
mechanism 19 is powered by a stepping motor 20 which enables
controlled movement of the build platform 17 in the z-axis (i.e. in
the vertical direction). The elevator mechanism is therefore
capable of adjusting the separation between the working surface 14
of the vat 13 and the planar surface 26 of the build platform 17,
the separation being the distance in the vertical direction (i.e.
the direction normal to the planar surface and normal to the
working surface of the vat).
The rotation mechanism takes the form of a rotatable plate 7 onto
which the vat 13 is mounted. The rotatable plate is circular and is
connected to a stepping motor 10. The stepping motor controls the
rotation of the circular plate and therefore the rotation of the
vat in a controlled manner about an axis which is normal to the
working surface at the floor of the vat.
The vat 13 includes an integral plug 25, and the rotatable plate 7
includes an aperture 24 (i.e. a cut-out) the plug 25 being
configured to engage the aperture 24 to secure the vat 13 to the
rotatable plate 7. As the plugs 25 are made from liquid silicone
rubber they can deform into the apertures 24, thus fastening the
vat 13 in place without the use of complex mechanisms. Furthermore,
the apertures 24 and plugs 25 allow for quick and easy removal of
the vat 13.
In the embodiment shown in FIG. 2, the axis of rotation about which
the relative rotation occurs is the central axis of the rotatable
plate 7.
The vat consists of a floor and surrounding walls, the floor
including a first floor portion 14 having a first thickness and a
second floor portion 15 having a second floor thickness, the second
thickness being less than the first thickness. In this way, when
the vat is filled with liquid photosensitive polymer the first
floor portion is a raised working surface, and the second floor
portion forms a deeper channel of photosensitive polymer.
The apparatus includes a source of electromagnetic radiation in the
form of a digital projector 21. The digital projector 21 consists
of a 405 nm LED, a spatial light modulator and a projection lens.
The 405 nm LED can be turned on and off independently of turning
the spatial light modulator on and off. The preferred spatial light
modulator is a DMD however any spatial light modulator such as LCD,
LCOS etc. could be used. The digital projector 21 is located such
that the projected image fits within the bounds of the apertures 6
and 8 so that the projected image is in focus at the raised working
surface 14. The size of the working surface 14 and the build
platform 17 are slightly larger than the size of the projected
image at the raised working surface 14. The apparatus is controlled
by a networked computer 22, which receives the 3D object data over
a network and synchronises the output of the stepping motors 10 and
20 and the projector 21 it also providing updates on the progress
of the fabrication to other networked computers. Enclosing the top
half of the apparatus 1 is a cover 23, which is fabricated from a
transparent material that blocks electromagnetic radiation with
wavelengths below 450 nm.
The apparatus 1 includes a frame 2, which has a bottom 3, a top 4,
sides 5 and an aperture 6. The rotatable plate 7 is located
directly above the top of the frame 5. The rotatable plate 7
includes an aperture 8 made from an optically clear material which
allows light from the projector 21 to get to the vat 13. The
rotatable plate 7 sits on casters 9 so that the rotatable plate is
free to rotate.
Referring to FIG. 3, the vat 13 is either entirely fabricated from
optically clear liquid silicone rubber (FIG. 3A) or the first floor
portion 14 is fabricated from optically clear silicone pad and set
into the second floor portion 15 that is fabricated from a stiffer
non-optically clear liquid silicone rubber (FIG. 3B). The optically
clear silicone pad which forms the first floor portion may be
replaceable or may be permanently fixed to the second floor
portion. Both types of vat are suitable for use with all of the
apparatuses described herein.
It is crucial that the vat 13 is fabricated from a material that
inhibits the cure of the liquid photosensitive polymer. The
preferred material is generically referred to as liquid silicone
rubber (LSR). More specifically, it is an addition cured vinyl
terminated-polydimethylsiloxane, where the catalyst is
platinum.
Phenyl resins are preferably added to the vat material to ensure
that the optically clear silicones do not yellow under UV light.
This is particularly advantageous where light of 405 nm is used.
The optical grade of the LSR used is preferably QSIL 216 although
QSIL 218 may also be used.
Where a stiffer non-optically clear liquid silicone rubber is used,
due to its high tear strength and elastic modulus, MM 730FG is a
suitable grade. In this way, the non-optically clear parts of the
vat will be relatively stiff and will not deform easily. This is
especially true for a wall thickness of at least 5 mm. MM260 grade
may also be used.
In operation, the cross-sectional data of the 3D model and a
configuration file is transferred to the controlling computer 22 by
the user over a network. The vat 13 is then filled with liquid
photosensitive polymer 16 up to a prescribed level. Once the
operator has confirmed that the vat 13 has sufficient
photosensitive polymer 16 to fabricate the desired 3D object and
that the build platform 17 is clean and securely fastened to the
elevator mechanism 19 the fabrication process begins. Checking of
the photosensitive polymer 16 level may be done manually by eye or
using a liquid depth sensor (not shown).
At the beginning of each fabrication the following calibration
process is carried out. The calibration process ensures that all
subsequent cross-sections are of the desire thickness.
As shown in FIG. 4A, the rotatable plate 7 is rotated to its start
position by a first stepper motor 10. The start position is defined
as the working surface 14 of the vat being located under build
platform 17 and the apertures 6 and 8 being coincident. The start
position may be defined by a micro-switch (not shown) located on
the elevator mechanism. Thus, when the elevator mechanism reaches
the start position, the micro switch is triggered. The elevator
mechanism 19 and a second stepper motor 20 (not shown in FIG. 4)
then move the build platform 17 to its start position at which the
face of the build platform 26 is located beneath the surface of the
photosensitive polymer 16 so that a layer of photosensitive polymer
27 less than 1 mm is sandwiched between the planar surface 26 of
the build platform 17 and the working surface 14. Again a micro
switch may define this start position (not shown).
The digital projector 21 then projects an image that is the maximum
size of the photo mask onto the layer of photosensitive polymer 27
thereby curing it onto the planar surface 26 of the build platform
17. The duration of exposure of this first layer can be in the
order of a minute.
As shown in FIG. 4B, after exposure, due to the oxygen richness of
the liquid silicone rubber vat 13, which inhibits the cure of
acrylate polymers, a lubricating layer 28 of uncured photosensitive
polymer exists between the working surface 14 and the cured
photosensitive polymer 29. This means that the cured photosensitive
polymer has not formed a bond with the raised working surface
14.
As shown in FIG. 4C, the circular plate 7 is then rotated 180
degrees positioning the second floor portion (the deeper channel)
15 below the build platform 17. This increases the depth of uncured
photosensitive polymer 16 between the cured photosensitive polymer
29 and the vat 13 thus the separation forces decreases and the
elevator mechanism 19 can easily move the build platform 17 up by a
distance defined by the cross-sectional thickness of the layers of
the 3D model.
As shown in FIG. 4D, the rotatable plate 7 is then rotated a
further 180 degrees, resulting in re-positioning of the working
surface 14 beneath the build platform 17 and also recoating the
working surface 14 with a fresh layer of photosensitive polymer 16.
This means that there is a layer of photosensitive polymer 30
between the raised working surface 14 and the face of the build
platform 26 that corresponds to the desired thickness of the
specific layer or cross section of the 3D model.
After calibration, the following printing process is carried
out:
1. The digital projector 21 exposes the layer of photosensitive
polymer 30 to the first `2D` cross section as shown in FIG. 2. The
exposure time depends on the desired thickness of the cross
section.
2. After exposure, and as described above, there exists a
lubricating layer on uncured photosensitive polymer 28. The
circular plate 7 rotates 180 degrees as shown in FIG. 4C
positioning the deeper channel under the build platform 17.
3. The build platform 17 is raised by the elevator mechanism 19 by
desired cross-sectional thickness of the next layer.
4. The circular plate 7 rotates back 180 degrees repositioning the
working surface 14 under the build platform and re-coating the
build platform with fresh photosensitive polymer that is the
thickness of the next cross-section 30 as shown in FIG. 4D.
5. During steps 2-4 the 405 nm LED is turned off by the controlling
computer 22 and the controlling computer 22 prepares the next cross
section to be displayed and sends this to the digital projector
21.
The above process is repeated until the final cross section is
completed to create the final material layer of the three
dimensional object.
Once fabrication of the three dimensional object is completed, the
elevator mechanism 19 moves to an end position located at the top
of the apparatus 1. This allows the easy removal of the build
platform 17 using the quick release mechanism 18. The three
dimensional object needs to be removed from the build platform 17
and cleaned. Whilst this occurs a second build platform 17 can be
attached to the elevator mechanism 19 and the photosensitive
polymer 16 level in the vat 13 can be checked to ensure the
apparatus 1 is ready to fabricate the next three dimensional
object.
FIG. 5 shows a second embodiment which differs from the first
embodiment in that it further comprises a heating element 11, which
has an aperture 12 that sits in between the rotation mechanism 7
and the vat 13 such that the apertures 8 and 12 are coincident and
beneath the raised working surface 14.
In operation, the heating element 11 is turned on before
calibration in order to heat up the resin 16 to a temperature of
40-90.degree. C., the temperature depending on the formulation of
the photosensitive polymer. A controlling computer 22 regulates the
temperature of the heating element 11. At the end of fabrication
the heating element is turned off and the photosensitive polymer 16
returns to room temperature.
The temperature of the photosensitive polymer needs to be precisely
controlled in order to avoid the production of any vapours, which
could be potentially unpleasant; this is achieved by the
controlling computer.
FIG. 6 depicts a third embodiment, where like reference numerals
are used to label the same features as the previous embodiments.
The third embodiment differs from the first embodiment in that
relative rotation of the vat and the build platform is achieved by
a rotation mechanism arranged to rotate the build platform 17.
The rotation mechanism takes the form of a first stepper motor 10
attached to the elevator mechanism 19. The build platform 17 is
attached to the first stepper motor 10 by quick release mechanism
18. In this embodiment, the axis of relative rotation is the
central axis of the first stepper motor 10. The controlling
computer 22 controls the rotation of the build platform about this
central axis.
In this embodiment, there is no need for a rotation mechanism. The
frame 3 includes an aperture 124 and the plug 25 is configured to
engage the aperture 124.
A fourth embodiment is shown in FIGS. 7 and 8. This embodiment
shares most of the features of the first embodiment but differs
from the first embodiment in that a z-axis assembly (including the
elevator mechanism 19, the build platform 17, the quick release
motor and the second stepper motor 20) is located on top of the
rotation mechanism 7 such that the rotation of the first stepper
motor 10 has the effect of rotating the z-axis assembly 30. The vat
13 is in a fixed position on the top of the frame 4.
The operation of the system is similar to that described above,
with the exception that it is the z-axis assembly 30 that rotates
during the relative rotation and the vat 13 remains in a fixed
position. This embodiment is advantageous in that the size of the
apparatus 1 is reduced. The torque required by the first stepper
motor 10 is also reduced, as is the duration of time taken between
the curing of each material layer.
The operation of this embodiment is shown in FIGS. 8A, 8B, and 8C.
The vat 13 is shown in FIG. 8A. with the working surface 14 of the
first floor portion fabricated from optically clear liquid silicone
rubber and the deeper channel 15 of the second floor portion. As
shown in FIG. 8B, after a layer has been cured onto the build
platform 17 the z-axis assembly 30 rotates 120 degrees about its
central axis. This moves the build platform 17 from the raised
working surface 14 into the deeper channel 15. The elevator
mechanism 19 then moves the build platform 17 up by the desired
thickness. As shown in FIG. 8C, the z-axis assembly then rotates
back 120 degrees thereby moving the build platform back over the
raised working surface at the new height thereby re-coating the
build platform with fresh photosensitive polymer ready for
fabrication of the next material layers.
120.degree. is the minimum angle of rotation required for the build
platform to have moved completely away from the working surface.
The angle could range between 120.degree.-360.degree., but is
preferably selected 120.degree. as this leads to the shortest
distance and therefore advantageously reduces the duration of time
taken between layers for the overall print process.
Referring to FIGS. 9A, 9B and 9C, a third type of vat is shown
which is suitable for use with any of the apparatuses described
herein. The vat of FIGS. 9A, 9B and 9C is similar to that of FIG.
3B in that it includes a replaceable optically clear silicone pad.
However, it differs from the first and second vats shown in FIGS.
3A and 3B in that the vat of FIG. 9A is not made entirely from
silicone.
As shown in FIGS. 9A, 9B and 9C, the vat comprises a vat body 13
and an optically clear silicone pad 32. The vat body 13 including a
recessed section 31, and the optically clear silicone pad
configured to be located in the recessed section.
The optically clear silicone pad 32 forms a first portion 14 of the
floor of the vat which corresponds to a raised working surface of
the floor of the vat. The remainder of the vat body 13 forms the
second portion of the floor of the vat 15 as well as the
surrounding walls of the vat. When the optically clear silicone pad
is located in the recessed section 31 of the vat body, the raised
working surface formed by the optically clear silicone pad is
located at least 1 mm above the deeper channel of the second floor
portion.
The recessed section 31 is fabricated from an optically clear
material (preferably a thermoplastic) that is positioned such that
when the vat 13 is fixed to the apparatus of any of the embodiments
described above, the apertures in the frame, rotatable plate and
heating element 6,8 and 12 lie are aligned with the recessed
section 31.
The vat body 13 of the vat may be fabricated from any suitable
material such as a thermoplastic. A water tight seal can be created
between the first floor portion of the optically clear silicone pad
and the second floor portion of the vat body 13.
In a further embodiment (not shown), the apparatus may take the
form of any of the previously described embodiments, but the
projector 21 is replaced with any directional source of
electromagnetic radiation. This may be, for example a scanning
laser or an array of LEDs.
While the invention has been described in conjunction with the
exemplary embodiments described above, many equivalent
modifications and variations will be apparent to those skilled in
the art when given this disclosure. Accordingly, the exemplary
embodiments of the invention set forth above are considered to be
illustrative and not limiting. Various changes to the described
embodiments may be made without departing from the spirit and scope
of the invention.
* * * * *